What it is: The Johnson & Johnson Official 7-Minute Workout app was designed by Chris Jordan, Director of Exercise Physiology at the Johnson & Johnson Human Performance Institute. It's designed to meet the American College of Sports Medicine's fitness guidelines, and includes both aerobic and strength-training exercises done in the style of a quick, fitness-building interval program. Best for: Beginners. This app ranks very highly on safety, making it a great choice for beginners. It provides an effective full-body workout that can help people meet fitness guidelines, but doesn't particularly excel in any one area. So anyone seeking a more specialized, less general program may want to look elsewhere. Relevant scores: 16.3 out of 30 for aerobic training; 17.2 out of 30 for strength trainingWhat it is: The Nike+ Training Club app includes more than 100 workouts designed by Nike trainers, with video and audio guidance for workouts of different lengths. You can also log your other fitness activities on the app. Best for: Full-body strength training. This app doesn't perform as well in the aerobic exercise portion (Nike has another app exclusively for running which is worth checking out). But it did well in the strength section. Reviewers noted that both the individual workouts and the multi-week training programs were good. Nike+ is great for tracking overall fitness and offers good strength-training options. This app is a promising choice if you want a varied selection of workouts using anything from simple body-weight exercises to gym equipment. And unlike most apps, there's no pressure to upgrade to a premium program. Relevant scores: 10 out of 30 for aerobic training; 19.5 out of 30 for strength training; 3.1 out of 10 for flexibilityWhat it is: This app was named Running for Weight Loss: Interval Training when it was reviewed for the study, but that's since changed. It's specifically focused on interval training, with runs that alternate between easier and harder levels of intensity. There's also a meal-planning component, which is important for weight loss. Best for: Aerobic training and running. This app is targeted towards people who want to lose weight, but it'll also help you build endurance and speed as a runner. Interval training is one of the best ways to get in shape, so no matter what your aerobic fitness goals are, plans that incorporate this approach are worth considering. The app also includes training programs for specific runs: one helps you prepare for a 5k within seven weeks, and another is a 16-week marathon training program (which assumes you already run a fair amount). Another program is designed for those just starting to run. To get to the free version, you need to sign up for a free premium trial and cancel the auto-renew. Some users report that the pop-ups asking you to sign up for a paid membership are intrusive. Relevant scores: 26.7 out of 30 for aerobic training; 3.5 out of 10 for flexibilityWhat it is: The free version of the app, which was formerly called Fitness Buddy Free, offers a range of workouts that can be done at home or in a gym using weights, a kettlebell, or a resistance band. Best for: Strength training. This is an app best used for strengthening work, though there are a couple of cardio and flexibility options. (Some flexibility exercises may have been added after the study reviewers did their work, so were not factored into the score.) You can also build custom workouts using a variety of exercises. Relevant scores: 8.1 out of 30 for aerobic fitness, 22.9 out of 30 for strength training.What it is: StrongLifts 5x5 is a specific, straightforward weight-training program based on five types of lifts: the squat, bench press, deadlift, overhead press, and barbell row. The program involves three workouts a week, with participants gradually increasing the amount of weight they can lift. Best for: Strength training, especially weight lifting. This is an excellent training program for people looking to get started with lifting, since it includes a series of exercises that serve as an excellent foundation for strength. There is also a premium version that includes additional exercises and warm-ups, but the basic training program is free and effective. Relevant scores: 24 out of 30 for strength training.What it is: Fitness Builder offers a variety of free, multi-week training plans (there's also an optional paid subscription). Free plans include over 400 workouts that can be solely body-weight based, rely on gym equipment, or fall somewhere in between. Best for: A strength- and flexibility-focused workout program. With a wide variety of plans, you can work through training programs focused on strength, movement, fat loss, and much more. Relevant scores: 21.2 out of 30 for strength training; 7.1 out of 10 for flexibility.What it is: The free version of this app, which used to be called Simply Yoga Free, offers yoga workout sessions of 20, 40, or 60 minutes. Best for: Flexibility. The free version of the app offers a pretty straightforward set of three predefined routines, with each move demoed by a personal trainer. There's not a ton of variety, but the routines include more than 30 poses for you to work through. Relevant scores: 6.4 out of 10 for flexibility.What it is: This app, which was called Daily Yoga-Lose Weight, Get Relief when the study was conducted, offers what's now a broad range of yoga sessions. Many of these are locked behind a paid membership, but certain beginner programs are included for free, as are a number of different yoga sessions. Best for: Flexibility. Within the free options, there's a good amount of variety for someone who wants to casually engage with yoga on their own at home. Relevant scores: 6.2 out of 10 for flexibility.You don't need to download or try everything here, especially at the start of a fitness routine. Remember that in general, to meet basic fitness guidelines, you should try to work out at least three days per week, with an average of at least 30 minutes every day. From there, choose something you are interested in and give it a shot. If these apps don't meet your needs, there are plenty more out there. While the apps on this list correspond best to the ACSM guidelines for a fitness program, everyone needs something different. Cyclists or runners with a regular routine might prefer to use something like Strava or MapMyRide to simply track their workouts, for example. Whatever you do, find a workout you enjoy enough to keep doing it regularly.